Vibration suppressing suspension for tensioned filaments of electron space charge devices



Jan. 11, 1949. I w 2,458,534

VIBRATION SUPPRESSING SUSPENSION FOR TENSIONED FILAMENTS 0F ELECTRON SPACE CHARGE DEVICES Filed June 29, 1946 INVENTOR F? SCHWERIN J m k ATTORNEYS.

Patented Jan. 11, 1949 VIBRATION SUPPRESSING SUSPENSION FOR TENSIONED FILAMENTS OF ELECTRON SPACE CHARGE DEVICES Paul Schwerin, White Plains, N. Y., assignor to Sonotone Corporation, Elmsford, N. Y., a corporation of New York Application June 29, 1946, Serial No. 680,357

1 Claim. 1

This invention relates to electron space discharge devices in which an electrode assembly comprising a cathode, an anode and at least one grid electrode interposed between the cathode and anode are enclosed in a hermetically sealed envelope and more particularly to such electron discharge devices which are known commercially as miniature and subminiature electron tubes and which utilize a thermionic filamentary element as the cathode.

Among the objects of the invention is a tube of the foregoing type in which the filamentary cathode is held in its operative position by a resilient tensioning member engaging an end part of the mounting portion of the cathode filament for. biasing a seating portion of the filament mounting element against a border edge of a spacer member of the electrode assembly, a part of the mounting portion of the cathode filament projecting beyond the edge of the spacer member being ofiset in a direction transverse to the direction of the seating element facing the edge, so that substantially the entire length of the seating element facing the spacer edge is held in engagement therewith for producing a damping action which suppresses microphonic vibrations of the filament.

The foregoing and other objects of the invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings wherein Fig. 1 is a side elevational view of a typical subminiature tubeythe tube being shown on an enlarged scale, such tubes having a length of only one inch or less;

Fig. 2 is an elevational view of the electrode assembly mounted in the interior of the tube with parts of the structure broken away;

Fig. 3 is a top View of Fig. 2; and

Figs. 4 and 5 are views similar to Fig. 2 showing successive stages of the process of tensioning and shaping the filament suspension elements.

There are many applications requiring multielectrode electron amplifier tubes of the miniature and subminiature type having extremely small dimensions and able to operate with a high degree of uniformity and efiiciency. Among such applications are hearing aid amplifiers and radio broadcast receivers of a size small enough to be worn hidden in a pocket of the user and other applications, such as the field of proximity fuses in which space is at a premium.

Although the principles of the invention are applicable to other types of tubes, their application will be described in connection with a pentode-type tube shown in Figs. 1 to 3. It comprises a hermetically-sealed, evacuated tubular envelope II of material, such as glass, which encloses an electrode assembly, generally designated I 2, provided with a plurality of leads l3 which are hermetically sealed in the terminal wall portion I4 of the envelope to provide external circuit connection to the enclosed electrodes.

The cathode assembly l2 comprises a cathode shown in the form of a single longitudinally-extending filament l5, a control grid It, a screen grid IT, a spacer grid [8 and an anode structure [9. The several grid electrodes I6, l'l, l8 and the anode l9 are of the conventional type and form internested electrode elements which extend longitudinally in directions generally parallel to the common longitudinal axis of the electrode assembly and of the tubular envelope II. The cathode 15 forms the central element of the electrode assembly. and is formed of an oxide-coated metal filament.

The several grids l6, l1, l3 are made of very fine metal wire about .001 to .004" in diameter. The inner wire grid I6 is supported on two grid posts 26, the similar grid I1 is supported on two grid postsZ'l and the grid I8 is supported on two grid posts 28. The several grid posts 26, 21, 28 of such tubes are usually formed of metal wires about .012" to .025 in diameter. The electrodes and their posts are held supported in their operative position by two similar generally-fiat sheet-like insulating spacer elements 30, 3|, commonly made of a material having a high dielectric constant, such as mica, the spacer elements being provided with openings or holes in which the grid posts and the anchoring elements l9l of the anodes are anchored.

' In the tube shown, each of the two spacer elements 30,.3l has formed in its center an elongated hole 32 provided at one of its narrow ends with a V-shaped edge or border portion 33 against the corner portion of which an upper seating portion 36 and a lower seating portion 31 of the mounting portions 38, 39, respectively, of-

the filament are held for stably supporting in its operative position the principal part of the filamentary cathode I5 extending between the two spacer members 30, 3| and facing the operative parts of the other electrodes.

- The upper mounting portion of the cathode filament I5 is provided with a tab 4| which is secured in a conventional way, as by welding, to one end of a tensioning member 42 shown in the form of a spring wire, the other end of which is secured, as by welding, to the upwardly projecting end of one of the grid posts 28 which supports the spacer grid IS. The lower mounting portion 39 of the cathode filament I is shown held in its operative position by one end of a tab 43 which is, in turn, held secured to a supporting projection 44 .mounted on and projecting outwardly from the lower insulating support member 32 of the electrode assembly.

The tab support 44 is of the conventional type and, as indicated in Figs. 2 and 3, it is formed by threading a thin strip of a metal, such as nickel, through two holes underlying the holes of the lower supporting member 3| and folding the strip along the outwardly facing surfaces of the supporting sheet member 3|, th end portions of the strip being folded over each'otherand formed into the downwardly projecting tab projection 44.

For the satisfactory operation of such tubes, it is important that the effective portion of the filamentary cathode l5 facing the other electrodes and extending between the two spacer supports 30, 3| shall be held stretched in a =definite operative position with respect to the :other electrodes. To this end, the tensioning wire d2 is made of a material having sufiicient stiifness and it is so arranged as to apply to the mounting portion 38 of the cathode filament connected thereto a biasing force which maintains the effective filamentary portion liextending between the two spacer supports 3ll,3| in stretched condition and at the same time holds the seating portions 36, 31 biased against the sharp corner of the V-shaped notch forming the seat against which the seating portions 36, 37

of the thin filament are held.

Prior art subminiature tubes provided with a filamentary cathode held in its operative positionby two spaced insulating supports, such as the mica supports 30, 3| of the electrode/assembly described above, presented serious manufacturing difficulties because the cathode filaments of a great many of the tubes 'manufactured'in accordance with long-establishedprior-artfpractice exhibited a tendency to vibrate, thus becoming the cause of disturbing microphonics. In all such prior tubes, the mounting portion of the filament was held against the border edge of the support opening 32 in the manner indicated in Fig. 4, the mounting portion of the filament was held against the border edge of -thesupport opening 32 in the mannerindicated in Fig. 4, the mounting portion of the filament passing'through the support opening 32 coming into engagement only with a relatively sharp edge of the border region of the support opening facing'the seating portion 38 of the filament. "The critical nature of the microphonic difficulties referred to "above "became even more aggravating in tubes in which a material, such as tungsten,was used asa filament core in lieu of the conventional nickel filament cores.

The invention is based on the discovery that the difficulties encountered with prior-art tubes by reason of cathode filament microphoni'cs are overcome and microphonic vibrations of the cathode filament are suppressed by iproviding'at least one of the two mounting supports of the filamentary cathode with an ofis'et portion of the type indicated on the mounting portion 38 at 38-4 extending in a direction transverse 'to the direction of the adjacent seating element 36 thereof, so as to assure that the forces *applied by the tensioning spring member 42 tothe mounting portion of the filament and transmitted thereby to the seating portion 36 of the filament are of such character as to cause substantially the entire length of the seating element 36 of the filament to cling and remain in contact engagement with the entire width'of the support seat 33 formed by the relatively wide .eclge surface of the spacer element 30 for damping and dissipating vibratory energy imparted to the filament, while .at.the same time maintaining the forces transmitted to the effective portion of the cathode filament |'5 extending between the two spacers 30, 3| sufficient to hold it in stretched condition.

In particular, it was found that when using cathode filaments of a refractory material, such as tungsten, which notwithstanding its small thickness of only .0005 in diameter, exhibits relatively great stiffness, the tensioning forces applied thereto by the tensioning Wire 42 in orderto maintain it stretched along the intermediate portion extending between the two spacer members 30, 3| will cause it to become curved along its seating portion '36 passing through the opening 32 of the spacerand maintam-contactengagementwith the seating-surface 33 only along its upper edge, in the manner indicated in Fig. 4, unless a lateral offset, such as indicated a 38-1 in Figs. *2 and 5 was formed in the mounting portion 38-ofthe filament.

In other words, the invention is based on the discovery that providing a lateral ofiset in the filament mounting portion extending between the seating portion of the filament and its point of connection to the tensioning member '52 makes itpossible to limit "the forces applied to "the seal;- ing region of the filament mounting portion to a value at which the effective portion of the cathode filament extending between its two supports 30, 3| holds it stretched while .at'the same time assuring that the forces transmitted by the tensioning means 42 to the seating portion 36 of the filament leave it in a straight condition and cause it to cling along its entire length against the facing relatively wide edge surface forming the seat 33 of the filament.

.-.As indicated in Fig. v2, .the offset ,portion 38-4 is formed on the part of .the filament mounting portion .adjoiningits seating portion 36 in order to assure that the biasing force transmitted from the tensioning spring 42 to the seating portion 36 .of the filament mounting portion exerts on the seating portion a :force which causes the entire length of the seating element .36 of 'the filament mounting portion to hug :the relatively full width of the facing iborder edge .33 of the supporting 1 sheet member 130. In other words, in the filament mounting arrangement of the invention, the forces which are imparted to the seating portion of the filament mounting portion are of such nature as to cause substantially the :entire length of the filament seating portion 35 to extend straight and substantially parallel to the facing seat border portion 33 of the spacer member 30. In this respect, the filament mounting arrangement of the invention diifersfrom the prior art'mounting arrangement in which the seating portion 36 of the filament was held positioned in the manner indicated in Fig. '4 and the forces exerted thereon caused the seating portion 36 to assume a curved configuration, only an-extremely short portion of the overall length of the seating element .35 being brought into engagement witha 'short element of the width of the facingborder portion 33 of the supporting sheet member 30.

It has been found in practice that it is sufficient to provide only one the filament mounting portions with a laterally ofiset portion, such as indi-v cated in Fig. 2 38-l, in order to effectively suppress microphonics encountered in a large fraction of the tubes heretofore manufactured and which had to be discarded. However, it may also be desirable to provide the lower mounting portion of the filament, such as indicated at 39 with a similar offset region in order to assure that the lower seating portion 37 of the filament mounting portion 39 has exerted thereon at the point at which it emerges from its contact engagement with the border edge of the filament support 32 a biasing force in a direction substantially perpendicular to the length of its seating portion 37.

In manufacturing tubes provided with a filament mount of the invention described above, one may proceed as follows:

After first assembling all electrodes, except the filamentary cathode electrode, into an electrode assembly including the support and spacer sheet members 30, 3 l as indicated in Fig. 2, the cathode filament l with its two tabs 4|, 43 previously secured to the ends of its mounting portion is threaded through the two holes 32 of the two spacer members 30, 3 I. lhereupon, the lower tab i3 is secured as byelectric spot welding to the supporting projection 44 extending from the lower spacer support 3!v Thereafter, the upper tab of the filament is secured to the tensioning spring 42 as by welding, While they are held in the position shown in Fig. 4. It is then merely necessary to bring a suitable deforming tool against the mountmg portion 38 of the filament emerging beyond the border of the support opening 32 and impart thereto the offset deformation 38I in the manner indicated in Fig. 5.

In order to enable those skilled in the art to readily practice the invention and without in any way limiting its scope, there are given below structural data of a subminiature tube of the invention.

The cathode filament was made of a wire of tungsten .0005" in diameter.

The upper tensioning spring 42 was formed of a spring wire .002" in diameter.

oThe thickness of the mica spacer was about .0 5".

The distance between the insulating spacers was of an inch.

It was found that by making the offset or kink 38-! only one millimeter long, substantially the entire length of the seating surface 36 of the filament mounting portion was held in contact engagement with substantially the entire width of the mica spacer in good vibration damping engagement therewith.

It will be apparent to those skilled in the art that the novel principles of the invention disclosed herein in connection with specific eXemplifications thereof will suggest various other modifications and applications of the same. It is accordingly desired that in construing the breadth of the appended claim it shall not be limited to the specific exemplifications of the invention described above.

I claim:

In an electrode assembly for an electron spacea discharge device: a set of electrodes including at least one control electrode; said electrodes extending longitudinally generally parallel to a common axis; said electrode assembly including a generally-flat sheet-like insulating spacer extending transverse to said axis and supporting the projecting end portions of said electrodes in their spaced operative positions; a metallic filament constituting the cathode and having a mounting portion extending from one end of said filament; said spacer having a spacer perforation through which said mounting portion extends and the border edge of said spacer perforation being of a width which is a multiple of the thickness of said filament; said electrode assembly including a resilient tensioning element connected to said mounting portion for stretching the portion of the filament facing the other electrodes and for biasing a seating element of said mounting portion toward a seat portion of said border edge; the major part of the length of said mounting portion extending in a direction generally paralle1 to said common axis; a part of said mounting portion projecting through the perforation toward said tensioning element being offset in a direction transverse to the direction of its length for limiting and controlling the direction of the tensioning forces exerted thereby on said seating element whereby substantially the entire length of said seating element is held in engagement with the facing border edge of the spacer for imparting to the filament a vibration suppressing damping action.

PAUL SCHWERIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,303,278 Ishler Nov. 24, 1942 2,350,003 West May 30, 1944 

